How does the age-specific death rate change as organisms grow older?

The age-specific death rate—the probability of an individual dying at a specific age—varies significantly across species and life stages, reflecting the complex biological process of aging.

In many species, including humans, the age-specific death rate is often described by the Gompertz function. This model demonstrates that mortality rates increase in a geometric progression, meaning they rise by a constant ratio over successive equal age intervals. As organisms grow older, they experience a progressive decline in biological functions and a reduced ability to adapt to metabolic stress, which makes them increasingly vulnerable to disease and death.12

However, the pattern of mortality depends on the species' life history:

• Type I: Species like humans exhibit low juvenile mortality, with the death rate remaining relatively low until it rises sharply in old age.3
• Type II: Some species experience a constant probability of dying at any age, resulting in a steady mortality rate throughout their life span.3
• Type III: Species that produce many offspring with little parental care often face very high mortality early in life, which decreases significantly for those that reach maturity.3